1. Field of the Invention
The present invention relates to a variable delay circuit. More particularly, the present invention relates to a variable delay circuit using a DLL circuit.
2. Description of the Related Art
A conventional variable delay circuit is configured with a rough delay circuit whose resolution is low and variable amount is large and a fine delay circuit whose resolution is high and variable amount is the same as the rough delay circuit. The rough delay circuit which takes the propagation delay time of a delay element as its resolution, and the fine delay circuit changes the delay amount by varying the load capacity of the delay element using a variable capacity element. And in order to prevent the delay precision from deteriorating due to the change of the propagation delay time caused by the noise or the change of the environmental conditions, it is proposed to configure the rough delay circuit with a DLL circuit (cf. International Publication Pamphlet No. 03/036769).
However, in the variable delay circuit using the conventional DLL circuit, the fine delay circuit is provided out of the feed-back system of the DLL, so the delay precision deteriorates as it is impossible to comply with the effect of the noise of the DLL circuit or the change of its environment such as the voltage or temperature.